Conventionally, for filmmaking, a film composition method using an optical technique is used when a motion picture film on which a foreground picture of, for example, a piece of furniture is imaged separately (hereinafter referred to as "foreground film") is superimposed on another motion picture film on which a background picture of, for example, a landscape is imaged (hereinafter referred to as "background film").
In this method, a foreground film is first used to make a motion picture film consisting of a pattern covering the area other than the foreground (hereinafter referred to as "female mask film") by optical means.
Then this female mask film is optically reversed to make a motion picture film having a mask pattern covering the portion in a background film corresponding to the foreground of the foreground film (hereinafter referred to as "male mask film").
A latent image of the foreground alone obtained by superposing the foreground film and the female mask film and a latent image of the background including no part of the foreground obtained by superposing the background film and the male mask film are superimposed on a raw film.
The foreground film and the background film are optically combined in this manner to make a motion picture film in which the foreground picture is superposed on the background picture.
The film composition method using this optical technique requires a complicated process for making various mask films and intermediate films and optically combining these films.
It is difficult to preestimate the final result during intermediate processing for making mask films and intermediate films and, in fact, a highly expert technique is required to obtain a predicted result in a short time.
A film composition method is therefore used in which conventional motion picture films are converted, by telecinematography, into video signals in accordance with high-definition television (HDTV) signals to effect electrical image composition on the video signals, and composite video signals thereby obtained are recorded on a film by an electron beam picture recording apparatus to combine foreground and background films, thereby making a combined motion picture film in which a foreground picture is superimposed on a background picture.
That is, as shown in FIG. 9, a background film F.sub.BK on which a background picture PIC.sub.BK is imaged is converted into a video signal through a telecinematographic unit 1A, thereby preparing a video tape T.sub.BK on which a background video signal VD.sub.BK is recorded.
Also, a foreground film F.sub.FR in which a foreground picture PIC.sub.FR is imaged on a so-called blue back B.sub.BK is converted into a video signal through a telecinematographic unit 1B, thereby preparing a video tape T.sub.FR on which a foreground video signal VD.sub.FR is recorded.
Video tapes T.sub.BK and T.sub.FR obtained in this manner are simultaneously played back by a video tape recorder (VTR), and a background video signal VD.sub.BK and a foreground video signal VD.sub.FR thereby obtained are input to a video signal composition unit 2 having a line-chromakey construction.
Video signal composition unit 2 is constituted by a mask signal generator 3 and a switching circuit 4. Background video signal VD.sub.BK and foreground video signal VD.sub.FR are supplied to first and second input terminals a and b of switching circuit 4.
Foreground video signal VD.sub.FR is also input to mask signal generator 3. Mask signal generator 3 then generates a male mask signal S.sub.MMSK for masking the area of foreground film F.sub.FR other than blue back B.sub.BK and supplies this signal to switching circuit 4 as a signal for changeover control of switching circuit 4.
Switching circuit 4 controls selection of the first or second input terminals a and b during one-line period of background video signal VD.sub.BK and foreground video signal VD.sub.FR in accordance with male mask signal S.sub.MMSK, and a composite video signal VD.sub.WA thereby obtained through an output terminal c is recorded by a VTR to make a video tape T.sub.WA.
Video tape T.sub.WA is played back at a low speed for electron beam picture recording by an electron beam picture recorder 5, and composite video signal VD.sub.WA is recorded on a raw film by electron beam picture recording.
Thus, background film F.sub.FR and foreground film F.sub.BK are combined to make a combined motion picture film F.sub.WA in which foreground picture PIC.sub.FR is superposed on background picture PIC.sub.BK.
In a case where a combined motion picture film is made by using the video signal composition processing technique as described above, it is necessary to convert background film F.sub.FR and foreground film F.sub.BK into video signals VD.sub.FR and VD.sub.BK, respectively.
There is therefore the problem of a deterioration of the image quality of the combined motion picture film F.sub.WA finally obtained relative to the qualities of the original motion picture films F.sub.FR and F.sub.BK due to limitation of the VTR band and other causes.
To solve this problem, a motion picture film composition method may be used in which only foreground film F.sub.BK obtained by imaging foreground picture PIC.sub.FR is converted into foreground video signal VD.sub.FR and the converted signal undergoes predetermined video signal processing, whereby advantages of film composition in terms of resolution and color development are maintained.
In this method, a mask signal is generated by a video signal composition technique using foreground video signal VD.sub.FR and is recorded on a film with an electron beam video recorder to facilitate mask film preparation most laborious and delicate in the film composition process.
That is, as shown in FIG. 10 in which components corresponding to those of FIG. 9 are indicated by the same reference symbols, foreground film F.sub.FR is converted into a video signal by telecinematographic unit 1B, and foreground video signal VD.sub.FR thereby obtained is recorded by a VTR to make video tape T.sub.FR.
This video tape T.sub.FR is played back at a low speed for electron beam picture recording by a first electron beam picture recorder 5A while being processed by reverse color composition, so that foreground video signal VD.sub.FR is recorded on a film by electron beam picture recording, thereby recording a second foreground film F.sub.FR1 consisting of a positive image corresponding to foreground film F.sub.FR.
Independently of this recording, video tape T.sub.FR is played back by a VTR and foreground video signal VD.sub.FR thereby obtained is input to mask signal generator 3 of video signal composition unit 2.
Mask signal generator 3 thereby generates male mask signal S.sub.MMSK masking the area of foreground film F.sub.FR other than blue back B.sub.BK, and this signal is recorded by a VTR to make a video tape T.sub.MMSK on which a male mask video signal VD.sub.MMSK is recorded.
Video tape T.sub.MMSK is played back at a low speed for electron beam picture recording by a second electron beam picture recorder 5B while being processed by black-and-white composition, so that male mask video signal VD.sub.MMSK is recorded on a film by electron beam picture recording, thereby recording a male mask film F.sub.MMSK.
A raw back-and-white film is exposed while superposing male mask film F.sub.MMSK on the raw film and is developed to form a female mask film F.sub.FMSK reversed from male mask film F.sub.MMSK.
Thereafter, according to this film composition method, an optical printer constituted by a main projector and a film camera is used in such a manner that foreground film F.sub.FR1 and female mask film F.sub.FMSK are set on the main projector by being superposed in a double superposition magazine called bi-pack, and a negative film in the film camera is exposed to the light image of these films.
Then, after the negative film in the film camera has been rewound, background film F.sub.BK and male mask film F.sub.MMSK are set on the main projector by a bi-pack, and the negative film in the film camera is exposed again to the light image of these films.
For this step, a so-called areal printer having two beam splitters may be used instead of the optical printer to perform exposure only one time for the same effect as the above operations.
In either case, a first latent image I.sub.L1 obtained by superposing foreground film F.sub.FR1 and female mask film F.sub.FMSK as described above and a second latent image I.sub.L2 obtained by superposing background film F.sub.BK and male mask film F.sub.MMSK are combined and developed to combine background film F.sub.BK and foreground film F.sub.FR, thereby making a combined motion picture film F.sub.WA1 in which foreground picture PIC.sub.FR is superposed on background picture PIC.sub.BK.
In the case of combined motion picture film F.sub.WA1 thus obtained, in contrast with combined motion picture film F.sub.WA obtained by video signal composition processing of video signals VD.sub.BK and VD.sub.FR of background films F.sub.BK and foreground film F.sub.FR as described above, background film F.sub.BK can be converted into a final combined picture without any restriction due to limitation of the VTR band, and it is possible to make superposed motion picture film F.sub.WA1 correspondingly improved in image quality, although a labor for making mask films F.sub.MMSK and F.sub.FMSK is required.
In the case of this motion picture film composition method, however, the timing of making second foreground film F.sub.FR1 by electron beam picture recording and the timing of making male mask film F.sub.MMSK actually differs from each other, and the characteristics of the electron beam picture recorders therefore vary slightly, resulting in occurrence of an error in determining the picture position or size in combined motion picture film F.sub.WA1 and, hence, failure to achieve a degree of film composition accuracy required for strict film superposition.
The characteristics of the electron beam picture recorders vary according to the increase in the temperature of the deflection yoke, drift of the deflection drive circuit, the difference between the vacuums of electron beam electrodes or other factors.